Thursday, November 26, 2009

Finding first broken build with git-bisect

With git it's so easy to find which commit broke the build. Suppose you know that commit with tag release-1.0 was good, i.e. all tests passed. The latest commit, however, is failing.

So the build was broken somewhere in between release-1.0 and master HEAD. To find the exact one you just need to run two git commands. First

$ git bisect start HEAD release-1.0

Here you specify which commit you know is broken, and which one you remember was successful. After running this command you can see that git marked two commits with good and bad labels, and put the search starting point at the revision in the middle.

The second command is git bisect run cmd, where cmd is the script used as a criterion of successful build. If you use Maven then your command would be:

$ git bisect run mvn clean test

After you hit Enter button in the terminal, git starts running your criterion script using binary search algorithm. It might take time to finish this task, which depends on the number of revisions and the execution time of the script. Eventually it stops and shows you which commit caused the build failure.